1. Field of the Invention
The present invention relates to a method of providing a phosphor with a precisely controlled element composition, a phosphor provided by the same, and a red phosphor that can emit red light after excitation and can be used in a device such as a display or a light emitting diode. The present invention also relates to a light emitting device comprising the said red phosphor.
2. Description of Related Art
With the increasing demand for environmentaly-friendly and energy-saving light-sources, many efforts are being contributed to develop light-sources with high-efficiency, energy-saving and eco-friendly attributes. Light-emitting diodes (LEDs) are mostly appreciated to be used to replace traditional light sources due to their compactness, low heat output, low energy consumption, long lifespan as well as less fragility, low contamination (e.g. Hg contamination) upon being discarded, and low energy consumption. In general, white light LEDs are composed of a blue light-emitting source with yellow phosphor. However, the white light generated by such LEDs may lack red light wavelengths and result in low color rendering property and low color saturation. Also, the inherent low light-emitting efficiency of yellow phosphor may cause low luminance to white light. In order to solve the above problems, composite phosphor composed of yellow phosphor mixed with red phosphor are proposed therefore to increase both the color rendering property for white lights and color saturation, since the adding of red phosphor may contribute to increase the luminance efficiency that is lacked by only employ of yellow phosphor.
Red phosphor, for example, can use Sr2Si5N8:Eu, CaAlSiN3:Eu, or sialon phosphor (i.e. MzSi12−(m+n)Alm+nOnN16−n). However, the use of Sr2Si5N8:Eu may decrease the color rendering property and color saturation since the Sr2Si5N8:Eu has a short lifespan. Although there is no deficiency of low lifespan with sialon phosphor, low luminance may incur while using sialon phosphor and therefore it is not well-used commercially. The CaAlSiN3:Eu has a long lifespan and a higher luminance than sialon phosphor has, but it still cannot satisfy the commercial need for high luminance and high lighting efficiency for the light emitting device.
The red phosphor of CaAlSiN3 Eu series, such as CamAlaSibNn:Euz (in which (m+z):a:b:n=1:1:1:3) or CabSicAldNn:Eua (in which a+b=1, 0.5≦c≦4, 0.5≦d≦8), can be provided by the steps shown below. A predetermined ratio of silicon nitride, aluminum nitride, calcium carbonate or calcium nitride, and europium oxide are mixed in a sintering holder, and then are sintered at 1700° C. of temperature, and greater than 10 atm of pressure under nitrogen atmosphere. The shortcoming of such method is that the high pressure (i.e. greater than 10 atm) may cause a dangerous explosion during manufacture, the manufacturing cost is increased due to the high cost of the equipment, and the color rendering property and the color saturation cannot be greatly increased due to the narrow wavelength range of the red phosphor. Besides, the required luminance cannot be obtained with the above method.
Therefore, it is desirable to provide an improved method to fabricate a red phosphor with a higher luminance and a higher light-emitting efficiency compared with a conventional phosphor of the same series, and which therefore can be further applied into the fabricating of white light LEDs having high color rendering property and high color saturation.